1. Field of the Invention
This invention relates to full extraction underground mining and more particularly relates to supporting gate entries and/or connecting openings during longwall or shortwall mining operations.
2. Description of the Related Art
The mining of minerals is a large industry with constantly developing technologies that improve the safety and efficiency of the mining operations. Technology is constantly being applied in the industry to reduce manpower, equipment needs, and costs.
In particular, underground mining carries constant risks to those who work underground. Of primary concern is the safety of the people working underground. Corporate interests and government regulations constantly monitor and evaluate the working conditions to ensure the utmost safety. Underground mining includes different types of full extraction mining. Full extraction mining is generally underground mining in which substantially all of the mined mineral is removed from the mine. Examples of full extraction mining include pillar mining, shortwall mining, longwall mining and the like. Examples of minerals that may be mined using full extraction mining include coal, potash, trona, salt, and the like. Although longwall mining is referenced herein as one example of full extraction mining those of skill in the art will recognize that embodiments of the present invention may be used in of various other types of full extraction mining.
Full extraction mining such as longwall mining may be conducted using an advancing method or a retreating method. In longwall retreat mining, a pair of tunnels are mined parallel to each other on each side of a mineral seam. These tunnels are generally referred to as gate entries, as longwall (or shortwall) entries, gate roads, or simply gates referred to herein as “a gate entry” or “gate entries.” The gate entries serve as the life line to the surface. The gate entries provide access for equipment and personnel, provide fresh air from the surface, provide two escape routes in case problems arise.
Keeping the gate entries open and safe is required for safe and efficient full extraction mining. Roof failure in gate entries is a major safety concern. Thousands of accidents occur each year due to roof failures. Roof supports are to protect the miners, but these supports can fail as well.
Due to the dangers involved, government regulations or corporate policies generally regulate how the gate entries are engineered, formed, and maintained as well as the technology and equipment used to support and keep the gate entries open and unobstructed. As full extraction mining is conducted, gate entries are susceptible to cave in of the roof and/or movement of the floor or walls which is collectively referred to herein as gate entry failure. Changes in the composition of the mineral or rock forming the roof, walls, or floor of the gate entry can also contribute to gate entry failures.
Conventional support systems for gate entries include installing and anchoring steel rods (roof, wall, or floor bolts), installing and anchoring steel cables (roof, rib, or floor cables), installing wooden or metal posts or cylinders against the floor and roof, applying glue or grout, installing concrete pillars and wedges, and/or installing steel beams or arches. These conventional support systems are installed throughout gate entries at great expense. All the materials used to support gate entries must be transported from the surface down to the gate entry within the mine. For example, the labor and material transportation costs can result in up to about $1,000 per foot. Furthermore the materials are typically very expensive. Adding to the cost of the materials, the conventional support systems are not removed once full extraction mining is complete due to the dangers to the workers.
In addition, certain conventional gate entry support systems are passive, meaning the support systems does not support a load until the gate entry roof or floor breaks apart and begins to fail. Furthermore, the passive gate entry support systems are installed and set manually by workers which increases the expense and time required to prepare the gate entry. Conventional support mechanisms provide only a limited support capacity. Often the support mechanisms must be replaced or reinforced repeatedly to provide adequate support. These support mechanisms can be very costly and, at times, ineffective at maintaining necessary safe access to the mining area.
One conventional support system includes a roof support integrated with a mining face conveyor. The mining face conveyor is a conveyor that carries a mineral away from a mining face. Consequently, the conventional support system is restricted to use within the mining face. Because the conventional support system is coupled to the mining face conveyor, the conventional support system is not capable of supporting a mine roof or floor within a gate entry independent of the mining face. Instead, the conventional support system ensures that the mining face conveyor remains in proper alignment with a transfer conveyor or stage loader. Unfortunately, this means that the conventional support system cannot be used independent of the mining face conveyor and/or a mineral transport conveyor. Furthermore, the conventional support system is unable to provide any support in gate entries that do not include the mineral transport conveyor and/or mining face conveyor. Finally, conventional support systems fail to provide support and facilitate airflow within gate entries.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method for supporting a gate entry for underground full extraction mining. Beneficially, such an apparatus, system, and method would be reusable, operate independent of a mining face conveyor, provide for both mine roof, mine walls, and mine floor support. Advantageously, such an apparatus, system, and method would provide for selective lateral support of gate entry walls. Such an apparatus, system, and method would also be mobile and comprise a minimal width profile to provide support while minimizing interference with the airflow within the gate entry. In addition, the apparatus, system, and method would form an access passage for personnel, equipment, and airflow that remains safely open during full extraction mining operations even as load abutments shift due to full extraction mining.